1. Field of the Invention
The present invention relates to optical plates, and more particularly to an optical plate typically used in a backlight module, the backlight module being used in apparatuses such as a liquid crystal display (LCD).
2. Discussion of the Related Art
In a liquid crystal display device, liquid crystal is a substance that does not itself radiate light. Instead, the liquid crystal relies on light received from a light source, in order that the liquid crystal can provide displaying of images and data. In the case of a typical liquid crystal display device, a backlight module powered by electricity supplies the needed light.
FIG. 7 represents a typical direct type backlight module 10. The backlight module 10 includes a housing 11, a plurality of lamp tubes 12, a light diffusion plate 13, a light diffusion sheet 14, and a prism sheet 15. The housing 11 includes a base 111, and a plurality of sidewalls 113 extending from a periphery of the base 111. Top ends of the sidewalls 113 cooperatively define an opening 112 therebetween. The light diffusion plate 13, the light diffusion sheet 14, and the prism sheet 15 are stacked in that order on the housing 11 above the opening 112. The lamp tubes 12 are positioned in the housing 11 under the light diffusion plate 13. Light rays emitted from the lamp tubes 12 are substantially diffused in the light diffusion plate 13, and finally surface light rays are output from the prism sheet 15.
However, to enhance the uniformity of light rays output by the backlight module 10, there must be a certain space between the light diffusion plate 13 and the lamp tubes 12. This space eliminates potential dark strips that may otherwise occur due to the reduced intensity of light between adjacent lamp tubes 12. Therefore the backlight module 10 may be unduly thick, and the overall intensity of the output light rays (luminance) may be reduced. Alternatively, the light diffusion plate 13 can be constructed to have sufficient thickness to be able to thoroughly diffuse light rays passing therethrough. In such case, the thickness is typically required to be in the range of about 2 to 3 centimeters.
In addition, the light diffusion plate 13 is typically manufactured by uniformly dispersing a plurality of light diffusion particles 132 into a transparent resin matrix material 131. Since numerous light rays are diffused by the light diffusion particles 132 a number of times in the light diffusion plate 13, an amount of light energy is lost, and a brightness of light output by the backlight module 10 is reduced.
Furthermore, the light diffusion plate 13, the light diffusion sheet 14, and the prism sheet 15 are in contact with each other, but with a plurality of air pockets existing at the boundaries therebetween. When the backlight module 10 is in use, light rays pass through the air pockets, and some of the light rays undergo total reflection at one or another of the corresponding boundaries. Thus the light energy utilization ratio of the backlight module 10 is reduced.
What is needed, therefore, is a new optical plate and a backlight module using the optical plate that can overcome the above-mentioned shortcomings.